Concern Grows Over Vanishing Horseshoe Crabs

John Tanacredi is asking for Long Island volunteers who will keep their eyes peeled for mating horseshoe crabs. He heads Dowling College’s annual inventory of the ancient marine arthropods.
Diane SanRoman

Romeo and Juliet had nothing on the magical, and these days often ill-fated, rendezvous that have occurred for millions of years up and down the East Coast shoreline under the full moons of spring and summer.
The rays from last weekend’s super moon, whose fullness coincided with our satellite’s perigee — its closest brush with Earth all year — surely plucked at the blue-blooded heartstrings of horseshoe crabs, guiding them close to shore in search of mates and enduring posterity. Both could be in jeopardy.
Dowling College in Oakdale is helping to guarantee their future through a Long Island-wide survey. Volunteers are needed.
The blood of these “living fossils” really is blue — not only a sign of their nobility, but because instead of hemoglobin it carries oxygen via copper-based hemocyanin. Their blood also contains amebocytes that guard against pathogens, making horseshoe crab blood an important tool in medical science. With a special state permit, laboratories may collect crabs, draw blood, and return them to the sea. Their value to science is relatively new in the total scheme of things.
Truly ancient are the animals themselves. Limulus polyphemus and three other varieties of horseshoe crab are said to be among the earth’s oldest living invertebrates. Fossils have been found in sedimentary rock from the late Ordovician period, about 450 million years ago. Not that far back, but old, is the animals’ link in a unique food chain that spans many thousands of miles and the discriminating tastes of wading shorebirds.
On moonlit nights in May and June, the “crabs,” which are actually arthropods more closely related to spiders and scorpions, enter shallow water. The female digs a hole in the sand. There is an unknown something in the grains that says, “This is the place.”
She lays her eggs, between 60,000 and 100,000 of them, in a number of smaller batches. The male, clinging on the female’s helmet-like shell from behind, fertilizes the eggs. They take about two weeks to hatch.
The red knot, ruddy brown in color and about the size of a blue jay, is a species of shorebird that times its migration from as far south as Tierra del Fuego to coincide with the horseshoe crabs’ mating season along the Eastern Seaboard. The knots arrive thin and hungry from their many thousands of miles on the wing. They gorge on the horseshoe caviar before moving on to their summer digs.
Turns out that “horsefeet,” as they are known in these parts, are about the best bait (when chopped in half) to lure conch into traps. Conchs, or welks, become scungilli when they are boiled from their shells and then steamed until tender.
The harvest of horseshoe crabs is strictly regulated by the Atlantic States Marine Fisheries Commission. Harvesters must be licensed in this state by the Department of Environmental Conservation. Fishermen are limited to 25 crabs per day, although the quota changes based on harvest numbers compiled from fishermen’s mandatory reports.
In 2004, in response to reports of a decline in the horseshoe crab population on Long Island and elsewhere, Dowling College began an annual survey. Dowling’s Center for Estuarine, Environmental, and Coastal Oceans Monitoring is now taking its 10th horseshoe crab inventory. The purpose of the survey is to gauge horseshoe crab population trends and habitat suitability along Long Island’s 600 miles of shoreline.
To participate, would-be volunteers can contact Sixto Portilla at PortillS@dowling.edu or John Tanacredi, Ph.D., at TanacreJ@dowling.edu.
Our local Limulus variety ranges from the Canadian maritime provinces to the Yucatan Peninsula in Mexico. There are only four varieties on Earth, three of which are in Asia, and two of these are in severe decline. On one of Japan’s southernmost islands, large crowds turn out to encourage a single breeding pair, according to Mr. Tanacredi.
Mr. Tanacredi, a world-renowned expert on horseshoe crabs, is chairman of Dowling’s department of earth and marine science and directs the monitoring program. In addition to the annual survey, Dowling raises and releases approximately 10,000 horseshoe crabs into the Great South Bay each year.
Loss of habitat is the biggest contributor to a decline in horseshoe crab numbers at a rate the Dowling survey puts at about 10 percent in just the past five years. Dowling’s survey volunteers check on 65 known breeding sites from Brooklyn to Montauk. In recent years, the most productive breeding area has been Plum Beach on Jamaica Bay in Brooklyn.
Last summer Mr. Tanacredi visited China, where he helped coordinate the first international conference on Asian horseshoe crabs at Hong Kong University. Chinese scientists visited Dowling College in 2007 in part to get a handle on the Asian crabs’ decline. The new Chinese National Museum of Marine Biology and Aquarium in Taiwan has a wing dedicated to the conservation of Asian horseshoe crabs, closely related to our own.
In Asia the crabs are harvested for scientific purposes, but, unlike the variety here, Asian horseshoes wind up on dinner plates throughout Southeast Asia and, although an acquired taste to say the least — “They’re pretty rough,” Mr. Tanacredi said — they are considered an exotic food.
“What’s happening is like hot dog vendors in Manhattan. There are stalls with a host of invertebrates to eat, including horseshoe crabs. If they’re gravid, their eggs are eaten like caviar. Just recently, an airline container at Kennedy Airport was found to contain hundreds en route to China.”
And, they are important culturally. In parts of China they are called “husband and wives” crabs and are considered an essential presence at weddings.
Mr. Tanacredi said that although Limulus was in better shape than its Asian cousins, loss of habitat was endangering them. Horseshoe crabs are harmless. That spiky tail is nature’s clever lever, used by overturned crabs to right themselves. It’s not enough to protect them from loss of habitat resulting from pollution and coastal development.
“There’s a slow, incremental, long-term reduction of the animals’ habitat, a chronic issue,” Mr. Tanacredi said. “That we could push them to extinction after all these years is a sad commentary.”